Proxy-based database scaling

ABSTRACT

Proxy-based scaling may be performed for databases. A proxy may be implemented for a database that can establish a connection between the proxy and a database engine to perform a database queries received from a client at the proxy. A scaling event may be detected for the database responsive to which the proxy may establish a connection with a new database engine which may, in some embodiments, have different capabilities or resources that address the features or criteria that triggered the scaling event. Session state may be copied from the database engine to the new database engine so that the new database engine may be able to provide access to the database on behalf of requests received from the client through the proxy.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 15/971,964, filed May 4, 2018, which claims benefit of priority to U.S. Provisional Application Ser. No. 62/590,171, filed Nov. 22, 2017, which are incorporated herein by reference in their entirety.

BACKGROUND

Commoditization of computer hardware and software components has led to the rise of service providers that provide computational and storage capacity as a service. At least some of these services (e.g., managed services such as managed relational database services) can be difficult to scale, including scaling the processing capacity. Disruption of an application or other process can be a high cost associated with changing capacity to better match workloads, as client applications may be interrupted due to dropped connections (and may not even retry to connect, in some instances). Techniques that can support scaling resources to match workloads therefore are highly desirable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a logical block diagram illustrating proxy-based database scaling, according to some embodiments.

FIG. 2 is a logical block diagram illustrating a provider network that implements a proxy service for databases accessed by a database service and stored in a storage service, according to some embodiments.

FIG. 3 is a logical block diagram illustrating a proxy service that implements a proxy for databases, according to some embodiments.

FIG. 4 is a logical block diagram illustrating a database service that implements proxy-based database scaling, according to some embodiments.

FIG. 5 is a logical block diagram illustrating a storage service that stores data for a separate database service, according to some embodiments.

FIG. 6 is a logical block diagram illustrating example client interactions to configure scaling events for a database, according to some embodiments

FIG. 7 is a block diagram illustrating the use of a separate storage service for a database service accessed via a proxy service, according to some embodiments.

FIG. 8 is sequence diagram illustrating a scaling event to change between different database engines, according to some embodiments.

FIGS. 9A and 9B are sequence diagrams to enter and exit a hibernation state for database using scaling events for the database, according to some embodiments.

FIG. 10 is high-level flowchart illustrating various methods and techniques to implement proxy-based database scaling, according to some embodiments.

FIG. 11 is high-level flowchart illustrating various methods and techniques to handle database access requests for a database in hibernation state, according to some embodiments.

FIG. 12 is a block diagram illustrating an example computer system, according to various embodiments.

While embodiments are described herein by way of example for several embodiments and illustrative drawings, those skilled in the art will recognize that the embodiments are not limited to the embodiments or drawings described. It should be understood, that the drawings and detailed description thereto are not intended to limit embodiments to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope as defined by the appended claims. The headings used herein are for organizational purposes only and are not meant to be used to limit the scope of the description or the claims. As used throughout this application, the word “may” is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). The words “include,” “including,” and “includes” indicate open-ended relationships and therefore mean including, but not limited to. Similarly, the words “have,” “having,” and “has” also indicate open-ended relationships, and thus mean having, but not limited to. The terms “first,” “second,” “third,” and so forth as used herein are used as labels for nouns that they precede, and do not imply any type of ordering (e.g., spatial, temporal, logical, etc.) unless such an ordering is otherwise explicitly indicated.

“Based On.” As used herein, this term is used to describe one or more factors that affect a determination. This term does not foreclose additional factors that may affect a determination. That is, a determination may be solely based on those factors or based, at least in part, on those factors. Consider the phrase “determine A based on B.” While B may be a factor that affects the determination of A, such a phrase does not foreclose the determination of A from also being based on C. In other instances, A may be determined based solely on B.

The scope of the present disclosure includes any feature or combination of features disclosed herein (either explicitly or implicitly), or any generalization thereof, whether or not it mitigates any or all of the problems addressed herein. Accordingly, new claims may be formulated during prosecution of this application (or an application claiming priority thereto) to any such combination of features. In particular, with reference to the appended claims, features from dependent claims may be combined with those of the independent claims and features from respective independent claims may be combined in any appropriate manner and not merely in the specific combinations enumerated in the appended claims.

DETAILED DESCRIPTION OF EMBODIMENTS

In various embodiments, proxy-based scaling for databases may be implemented. For example, a provider network or other database system or service may implement a database proxy (e.g., as a multi-tenant proxy for a plurality of databases on behalf of a plurality of clients) to serve as an intermediary connection between a database client and database. In this way, various database management operations may be performed without disrupting the connection of the client (e.g., leading to client application downtime, failures, service interruptions, etc.) and thus improving the performance of client processes or applications that utilize a connection to a database while also gaining the improvements offered by scaling resources implementing a database to meet desired performance or cost goals, in some embodiments. For example, a first client request for a given database may trigger an initial provisioning of computing resources of the database service for the given database, (which may also save resource costs by not provision computing resources for a database connection until that database connection is received, reducing idle computing resources and improving the efficiency of a database service or system as a whole). In another example, client requests can be monitored to establish application workloads for use in automated or intelligent resource provisioning to dynamically adjust resources for databases transparent to the applications based on the established application workloads, models of application workloads, or client profiles so that resources are not wasted when performing automated management of databases for a user, as discussed below with regard to FIGS. 6 and 8-11, which could improve the performance of a system implementing database as the response to changing system conditions would be significantly faster if handled using automated resource management instead of relying upon human involvement, in some embodiments.

Client applications may connect to a proxy over a network via a first network endpoint and send database requests to the proxy instead of the database engine or host directly, in some embodiments. The proxy may then identify a second network endpoint for the database engine to provide access to the database and establish a separate connection with the database engine, in some embodiments. The proxy may maintain open client application connections while database management operations are performed, in various embodiments. In this way, a client application may connect to the proxy independent of the underlying database architecture and avoid imposing modifications on client applications, in some embodiments. Furthermore, the client application may be unaware of the underlying database systems as the client may only communicate with the proxy because the proxy may maintain separate secure communications mechanisms for the client and the database service, (e.g., by separately encrypting and decrypting database requests independently between the client application and the database engine) which may prevent the client from having to reestablish a connection in the event of interruptions or other failures at the underlying database system, in some embodiments.

FIG. 1 is a logical block diagram illustrating proxy-based database scaling, according to some embodiments. In scene 102, client(s) 110 may establish a connection with proxy 120 so that proxy 120 may be able to receive or otherwise handle requests to access a database from client 110, in some embodiments. Proxy 120 may have established a connection with an appropriate database engine 130 (e.g., mapped to the client or database). In various embodiments, mapping information or other routing decisions for a database connection request may be determined according information additional to the connection request itself. Proxy 120 can then send database access requests received from client(s) 110 on to database engine 130. Database engine 130 may then access database data 140 to perform the query, in some embodiments, and provide a result to proxy 120. Proxy 120 may in turn provide a result for the access request to client 110, in some embodiments.

Because the behavior or requirements of client(s) 110 for a database may change over time, automation techniques may be implemented to monitor the database for a scaling event, as discussed below with regard to FIG. 10. For example, as illustrated in scene 104, a scaling event may be detected to move from database engine 130 to database engine 140 (which may offer more (or less) resources for use in performing access requests to the database from client(s) 110). Both database engines 130 and 140 may be able to access database data 160 as it may be stored in a separately accessible network-based data store, such as the storage service discussed below with regard to FIGS. 2, 5 and 7, or other data storage system that may be accessed by multiple database engines independently (or in succession), in some embodiments. Moreover, proxy 120 may copy session state 150 obtained from database engine 130 to database engine 140, in some embodiments. In this way, client(s) 110 may experience little disruption as a result of scaling the database engine to database engine 140, in some embodiments. As illustrated in scene 106, once the session state is copied, database engine 140 may take over providing access to the database data 160, replacing database engine 130. In this way, the more optimal configuration of database engine 140 (e.g., optimal in terms of resource or cost utilization) may be leveraged instead of database engine 130, in some embodiments.

Please note, FIG. 1 is provided as a logical illustration of clients, proxies, database engines, database data, and respective interactions and is not intended to be limiting as to the physical arrangement, size, or number of components, modules, or devices to implement such features. For example, in some embodiments, load balancing may be implemented to select a proxy, as discussed below with regard to FIG. 3 or a database may enter a hibernation state before being accessed again by a new database engine, as discussed below with regard to FIGS. 9A-9B and 11.

The specification first describes an example database service that utilizes proxies from proxy service to perform proxy-based scaling for databases. Included in the description of the example network-based database service are various aspects of the example network-based database service, such as a database engine head node, proxy service, including proxy nodes, and a separate storage service, including storage nodes. The specification then describes flowcharts of various embodiments of methods for implementing a proxy-based scaling for databases. Next, the specification describes an example system that may implement the disclosed techniques. Various examples are provided throughout the specification.

The systems described herein may, in some embodiments, implement a network-based service that enables clients (e.g., subscribers) to operate a data storage system in a cloud computing environment. In some embodiments, the data storage system may be an enterprise-class database system that is highly scalable and extensible. In some embodiments, queries may be directed to database storage that is distributed across multiple physical resources, and the database system may be scaled up or down on an as needed basis. The database system may work effectively with database schemas of various types and/or organizations, in different embodiments. In some embodiments, clients/subscribers may submit queries in a number of ways, e.g., interactively via an SQL interface to the database system. In other embodiments, external applications and programs may submit queries using Open Database Connectivity (ODBC) and/or Java Database Connectivity (JDBC) driver interfaces to the database system.

More specifically, the systems described herein may, in some embodiments, implement a service-oriented database architecture in which various functional components of a single database system are intrinsically distributed. For example, rather than lashing together multiple complete and monolithic database instances (each of which may include extraneous functionality, such as an application server, search functionality, or other functionality beyond that required to provide the core functions of a database), these systems may organize the basic operations of a database (e.g., query processing, transaction management, caching and storage) into tiers that may be individually and independently scalable. For example, in some embodiments, each database instance in the systems described herein may include a database tier (which may include a single database engine head node and a client-side storage system driver), and a separate, distributed storage system (which may include multiple storage nodes that collectively perform some of the operations traditionally performed in the database tier of existing systems).

As described in more detail herein, in some embodiments, some of the lowest level operations of a database, (e.g., backup, restore, snapshot, recovery, and/or various space management operations) may be offloaded from the database engine to the storage layer and distributed across multiple nodes and storage devices. For example, in some embodiments, rather than the database engine applying changes to database tables (or data pages thereof) and then sending the modified data pages to the storage layer, the application of changes to the stored database tables (and data pages thereof) may be the responsibility of the storage layer itself. In such embodiments, redo log records, rather than modified data pages, may be sent to the storage layer, after which redo processing (e.g., the application of the redo log records) may be performed somewhat lazily and in a distributed manner (e.g., by a background process). In some embodiments, crash recovery (e.g., the rebuilding of data pages from stored redo log records) may also be performed by the storage layer and may also be performed by a distributed (and, in some cases, lazy) background process.

In some embodiments, because only redo logs (and not modified data pages) are sent to the storage layer, there may be much less network traffic between the database tier and the storage layer than in existing database systems. In some embodiments, each redo log may be on the order of one-tenth the size of the corresponding data page for which it specifies a change. Note that requests sent from the database tier and the distributed storage system may be asynchronous and that multiple such requests may be in flight at a time.

In some embodiments, the systems described herein may partition functionality of a database system differently than in a traditional database, and may distribute only a subset of the functional components (rather than a complete database instance) across multiple machines in order to implement scaling. For example, in some embodiments, a client-facing tier may receive a request specifying what data is to be stored or retrieved, but not how to store or retrieve the data. This tier may perform request parsing and/or optimization (e.g., SQL parsing and optimization), while another tier may be responsible for query execution. In some embodiments, a third tier may be responsible for providing transactionality and consistency of results. For example, this tier may enforce some of the so-called ACID properties, in particular, the Atomicity of transactions that target the database, maintaining Consistency within the database, and ensuring Isolation between the transactions that target the database. In some embodiments, a fourth tier may then be responsible for providing Durability of the stored data in the presence of various sorts of faults. For example, this tier may be responsible for change logging, recovery from a database crash, managing access to the underlying storage volumes and/or space management in the underlying storage volumes.

In various embodiments, a database instance may include multiple functional components (or layers), each of which provides a portion of the functionality of the database instance. In one such example, a database instance may include a query parsing and query optimization layer, a query execution layer, a transactionality and consistency management layer, and a durability and space management layer. As noted above, in some existing database systems, scaling a database instance may involve duplicating the entire database instance one or more times (including all of the aforementioned layers), and then adding glue logic to stitch them together. In some embodiments, the systems described herein may instead offload the functionality of the durability and space management layer from the database tier to a separate storage layer, and may distribute that functionality across multiple storage nodes in the storage layer.

In some embodiments, the database systems described herein may retain much of the structure of the upper half of the database instance discussed in the example above, but may redistribute responsibility for at least portions of the backup, restore, snapshot, recovery, and/or various space management operations to the storage tier. Redistributing functionality in this manner and tightly coupling log processing between the database tier and the storage tier may improve performance, increase availability and reduce costs, when compared to previous approaches to providing a scalable database. For example, network and input/output bandwidth requirements may be reduced, since only redo log records (which are much smaller in size than the actual data pages) may be shipped across nodes or persisted within the latency path of write operations. In addition, the generation of data pages can be done independently in the background on each storage node (as foreground processing allows), without blocking incoming write operations. In some embodiments, the use of log-structured, non-overwrite storage may allow backup, restore, snapshots, point-in-time recovery, and volume growth operations to be performed more efficiently, e.g., by using only metadata manipulation rather than movement or copying of a data page. In some embodiments, the storage layer may also assume the responsibility for the replication of data stored on behalf of clients (and/or metadata associated with that data, such as redo log records) across multiple storage nodes. For example, data (and/or metadata) may be replicated locally (e.g., within a single “availability zone” in which a collection of storage nodes executes on its own physically distinct, independent infrastructure) and/or across availability zones in a single region or in different regions.

In various embodiments, the database systems described herein may support a standard or custom application programming interface (API) for a variety of database operations. For example, the API may support operations for creating a database, creating a table, altering a table, creating a user, dropping a user, inserting one or more rows in a table, copying values, selecting data from within a table (e.g., querying a table), cancelling or aborting a query, and/or other operations.

In some embodiments, the database tier of a database instance may include a database engine head node that receives read and/or write requests from various client programs (e.g., applications) and/or subscribers (users), then parses them and develops an execution plan to carry out the associated database operation(s). For example, the database engine head node may develop the series of steps necessary to obtain results for complex queries and joins. In some embodiments, the database engine head node may manage communications between the database tier of the database system and clients/subscribers, as well as communications between the database tier and a separate distributed storage system.

In some embodiments, the database engine head node may be responsible for receiving SQL requests from end clients through a JDBC or ODBC interface and for performing SQL processing and transaction management (which may include locking) locally. However, rather than generating data pages locally, database engine head node (or various components thereof) may generate redo log records and may ship them to the appropriate nodes of a separate distributed storage system. In some embodiments, a client-side driver for the distributed storage system may be hosted on the read-write node and may be responsible for routing redo log records to the storage system node (or nodes) that store the segments (or data pages thereof) to which those redo log records are directed. For example, in some embodiments, each segment may be mirrored (or otherwise made durable) on multiple storage system nodes that form a protection group. In such embodiments, the client-side driver may keep track of the nodes on which each segment is stored and may route redo logs to all of the nodes on which a segment is stored (e.g., asynchronously and in parallel, at substantially the same time), when a client request is received. As soon as the client-side driver receives an acknowledgement back from a write quorum of the storage nodes in the protection group (which may indicate that the redo log record has been written to the storage node), it may send an acknowledgement of the requested change to the database tier (e.g., to the read-write node). For example, in embodiments in which data is made durable through the use of protection groups, the database engine head node may not be able to commit a transaction until and unless the client-side driver receives a reply from enough storage node instances to constitute a write quorum.

In some embodiments, the database tier (or more specifically, the database engine head node) may include a cache in which recently accessed data pages are held temporarily. In such embodiments, if a write request is received that targets a data page held in such a cache, in addition to shipping a corresponding redo log record to the storage layer, the database engine may apply the change to the copy of the data page held in its cache. However, unlike in other database systems, a data page held in this cache may not ever be flushed to the storage layer, and it may be discarded at any time (e.g., at any time after the redo log record for a write request that was most recently applied to the cached copy has been sent to the storage layer and acknowledged). The cache may implement any of various locking mechanisms to control access to the cache by at most one writer (or multiple readers) at a time, in different embodiments.

In some embodiments, the client-side driver(s) running on the database engine head node may expose a private interface to the storage tier. In some embodiments, it may also expose a traditional iSCSI interface to one or more other components (e.g., other database engines or virtual computing services components). In some embodiments, storage for a database instance in the storage tier may be modeled as a single volume that can grow in size without limits, and that can have an unlimited number of IOPS associated with it. When a volume is created, it may be created with a specific size, with a specific availability/durability characteristic (e.g., specifying how it is replicated), and/or with an IOPS rate associated with it (e.g., both peak and sustained). For example, in some embodiments, a variety of different durability models may be supported, and users/subscribers may be able to specify, for their database tables, a number of replication copies, zones, or regions and/or whether replication is synchronous or asynchronous based upon their durability, performance and cost objectives.

In some embodiments, the client side driver(s) (may maintain metadata about the volume and may directly send asynchronous requests to each of the storage nodes necessary to fulfill read requests and write requests without requiring additional hops between storage nodes. For example, in some embodiments, in response to a request to make a change to a database table, the client-side driver may determine the one or more nodes that are implementing the storage for the targeted data page (e.g., based on storage metadata for the distributed storage system), and to route the redo log record(s) specifying that change to those storage nodes. The storage nodes may then be responsible for applying the change specified in the redo log record to the targeted data page at some point in the future. As writes are acknowledged back to the client-side driver, the client-side driver may advance the point at which the volume is durable and may acknowledge commits back to the database tier. As previously noted, in some embodiments, the client-side driver may not ever send data pages to the storage node servers. This may not only reduce network traffic, but may also remove the need for the checkpoint or background writer threads that constrain foreground-processing throughput in previous database systems.

FIG. 2 is a logical block diagram illustrating a provider network that implements a proxy service for databases accessed by a database service and stored in a storage service, according to some embodiments. A provider network may be a private or closed system or may be set up by an entity such as a company or a public sector organization to provide one or more services (such as various types of cloud-based storage) accessible via the Internet and/or other networks to clients 250, in some embodiments. The provider network may be implemented in a single location or may include numerous provider network regions, that may include one or more data centers hosting various resource pools, such as collections of physical and/or virtualized computer servers, storage devices, networking equipment and the like (e.g., computing system 2000 described below with regard to FIG. 12), needed to implement and distribute the infrastructure and storage services offered by the provider network within the provider network 200.

A number of clients (shown as clients 250 may interact with a provider network 200 via a network 260, in some embodiments. Provider network 200 may implement database service 210, storage service 220, proxy service 230, and/or one or more other virtual computing services 240. It is noted that where one or more instances of a given component may exist, reference to that component herein may be made in either the singular or the plural. However, usage of either form is not intended to preclude the other.

In various embodiments, the components illustrated in FIG. 2 may be implemented directly within computer hardware, as instructions directly or indirectly executable by computer hardware (e.g., a microprocessor or computer system), or using a combination of these techniques. For example, the components of FIG. 2 may be implemented by a system that includes a number of computing nodes (or simply, nodes), each of which may be similar to the computer system embodiment illustrated in FIG. 12 and described below. In various embodiments, the functionality of a given service system component (e.g., a component of the database service or a component of the storage service) may be implemented by a particular node or may be distributed across several nodes. In some embodiments, a given node may implement the functionality of more than one service system component (e.g., more than one database service system component).

Generally speaking, clients 250 may encompass any type of client that can submit network-based services requests to provider network 200 via network 260, including requests for database services. For example, a given client 250 may include a suitable version of a web browser, or may include a plug-in module or other type of code module may execute as an extension to or within an execution environment provided by a web browser. Alternatively, a client 250 (e.g., a database service client) may encompass an application such as a database application (or user interface thereof), a media application, an office application or any other application that may make use of persistent storage resources to store and/or access one or more database tables. In some embodiments, such an application may include sufficient protocol support (e.g., for a suitable version of Hypertext Transfer Protocol (HTTP)) for generating and processing network-based services requests without necessarily implementing full browser support for all types of network-based data. That is, client 250 may be an application may interact directly with network-based services platform 200. In some embodiments, client 250 may generate network-based services requests according to a Representational State Transfer (REST)-style web services architecture, a document- or message-based network-based services architecture, or another suitable network-based services architecture.

In some embodiments, a client 250 (e.g., a database service client) may be may provide access to network-based storage of database tables to other applications in a manner that is transparent to those applications. For example, client 250 may be may integrate with an operating system or file system to provide storage in accordance with a suitable variant of the storage models described herein. However, the operating system or file system may present a different storage interface to applications, such as a conventional file system hierarchy of files, directories and/or folders. In such an embodiment, applications may not need to be modified to make use of the storage system service model, as described above. Instead, the details of interfacing to provider network 200 may be coordinated by client 250 and the operating system or file system on behalf of applications executing within the operating system environment. Although client(s) 250 are illustrated as external to provider network 200, in some embodiments, internal clients, such as applications or systems implemented on other virtual computing resources may make use of a database hosted by database service 210 by accessing the database using a dynamic proxy implemented as part of proxy service 230.

Clients 250 may convey network-based services requests to and receive responses from provider network 200 via network 260. In various embodiments, network 260 may encompass any suitable combination of networking hardware and protocols necessary to establish network-based communications between clients 250 and network-based platform 200. For example, network 260 may generally encompass the various telecommunications networks and service providers that collectively implement the Internet. Network 260 may also include private networks such as local area networks (LANs) or wide area networks (WANs) as well as public or private wireless networks. For example, both a given client 250 and provider network 200 may be respectively provisioned within enterprises having their own internal networks. In such an embodiment, network 260 may include the hardware (e.g., modems, routers, switches, load balancers, proxy servers, etc.) and software (e.g., protocol stacks, accounting software, firewall/security software, etc.) necessary to establish a networking link between given client 250 and the Internet as well as between the Internet and network-based services platform 200. It is noted that in some embodiments, clients 250 may communicate with provider network 200 using a private network rather than the public Internet. For example, clients 250 may be provisioned within the same enterprise as a database service system (e.g., as part of another network-based service in provider network 200 which also offers database service 210 and/or storage service 220). In such a case, clients 250 may communicate with platform 200 entirely through a virtual private network 260 (e.g., a LAN or WAN that may use Internet-based communication protocols but which is not publicly accessible).

Generally speaking, provider network 200 may implement one or more service endpoints may receive and process network-based services requests, such as requests to access data pages (or records thereof). For example, provider network 200 may include hardware and/or software may implement a particular endpoint, such that an HTTP-based network-based services request directed to that endpoint is properly received and processed. In one embodiment, provider network 200 may be implemented as a server system may receive network-based services requests from clients 250 and to forward them to components of a system that implements database service 210, storage service 220 and/or another virtual computing service 230 for processing. In other embodiments, provider network 200 may be implemented as a number of distinct systems (e.g., in a cluster topology) implementing load balancing and other request management features may dynamically manage large-scale network-based services request processing loads. In various embodiments, provider network 200 may be may support REST-style or document-based (e.g., SOAP-based) types of network-based services requests.

Provider network 200 may implement various client management features. For example, provider network 200 may coordinate the metering and accounting of client usage of network-based services, including storage resources, such as by tracking the identities of requesting clients 250, the number and/or frequency of client requests, the size of data tables (or records thereof) stored or retrieved on behalf of clients 250, overall storage bandwidth used by clients 250, class of storage requested by clients 250, or any other measurable client usage parameter. Provider network 200 may also implement financial accounting and billing systems, or may maintain a database of usage data that may be queried and processed by external systems for reporting and billing of client usage activity. In certain embodiments, provider network 200 may collect, monitor and/or aggregate a variety of storage service system operational metrics, such as metrics reflecting the rates and types of requests received from clients 250, bandwidth utilized by such requests, system processing latency for such requests, system component utilization (e.g., network bandwidth and/or storage utilization within the storage service system), rates and types of errors resulting from requests, characteristics of stored and requested data pages or records thereof (e.g., size, data type, etc.), or any other suitable metrics. In some embodiments such metrics may be used by system administrators to tune and maintain system components, while in other embodiments such metrics (or relevant portions of such metrics) may be exposed to clients 250 to enable such clients to monitor their usage of database service 210, storage service 220, proxy service 230 and/or another virtual computing service 240 (or the underlying systems that implement those services).

In some embodiments, proxy service 230 and/or database service 210 may implement user authentication and access control procedures. For example, for a given network-based services request to access a particular database table, a proxy node may ascertain whether the client 250 associated with the request is authorized to access the particular database table. Provider network 200 may determine such authorization by, for example, evaluating an identity, password or other credential against credentials associated with the particular database table, or evaluating the requested access to the particular database table against an access control list for the particular database table. For example, if a client 250 does not have sufficient credentials to access the particular database table, the proxy node may reject the corresponding network-based services request, for example by returning a response to the requesting client 250 indicating an error condition. Various access control policies may be stored as records or lists of access control information by database service 210, storage service 220 and/or other virtual computing services 230.

Note that in many of the examples described herein, storage service 220 may be internal to a computing system or an enterprise system that provides database services to clients 250, and may not be exposed to external clients (e.g., users or client applications). In such embodiments, the internal “client” (e.g., database service 210) may access storage service 220 over a local or private network (e.g., through an API directly between the systems that implement these services). In such embodiments, the use of storage service 220 in storing database tables on behalf of clients 250 may be transparent to those clients. In other embodiments, storage service 220 may be exposed to clients 250 through provider network 200 to provide storage of database tables or other information for applications other than those that rely on database service 210 for database management. In such embodiments, clients of the storage service 220 may access storage service 220 via network 260 (e.g., over the Internet). In some embodiments, a virtual computing service may receive or use data from storage service 220 (e.g., through an API directly between the virtual computing service and storage service 220) to store objects used in performing computing services on behalf of a client 250. In some cases, the accounting and/or credentialing services of provider network 200 may be unnecessary for internal clients such as administrative clients or between service components within the same enterprise.

FIG. 3 is a logical block diagram illustrating a proxy service that implements a dynamic proxy for databases, according to some embodiments. Clients 310 may be similar to clients 110 in FIG. 1, clients 250 in FIG. 2, or other clients, such as internal clients or applications of provider network 200. Clients 310 may access database service 210 via one or more proxy node(s) 330 implemented as part of proxy service 230, in some embodiments.

Proxy service 230 may implement a load balancer 320, in some embodiments, which may apply one or more load balancing schemes (e.g., round-robin, hashing, least connections, etc.) to distribute connection requests from clients to different proxy nodes 330. For example, a connection from request to a database from client A may be directed to proxy node A to connect database A. A second connection to database A from client B may however be directed to proxy node B by load balancer 320, even though the databases are the same, in some embodiments. Load balancer 320 may be implemented by one or more computing nodes, servers, or other networking devices, such as computer system 2000 in FIG. 12. In at least some embodiments, a networking interface and/or network control service implemented as part of provider network 200 may, in some embodiments, implement private networks (or virtual private networks) within provider network 200 that include client(s) 310. Load balancer 320 may be able to implement requests directed a network interface or other network endpoint for the virtual private network of client 310 in order to direct requests through proxy service 230 to a virtual private network implementing a database engine in database service 210, in some embodiments.

Proxy service 230 may implement a fleet, pool, or group of one or more proxy node(s) 330 to provide access to database engines for client(s) 310, in some embodiments. Proxy nodes 320 may be implemented on one or more computing devices, servers, or other systems, such as computer system 2000 in FIG. 12 below), in some embodiments. Proxy node(s) 330 may implement a database interface 332 that corresponds, matches, or otherwise interprets requests from client(s) 310 in order to mimic or otherwise make the interactions between the proxy node 330 and the client 310 simulate a direct connection between client 310 and a database engine, in some embodiments. Proxy node(s) 330 may implement request processing 334, in some embodiments, to select various actions to perform based on the network traffic received from a client, such as by examining network packet metadata. In some embodiments, request processing 334 may perform encryption and decryption according to the encryption schemes implemented between client(s) 310 and proxy 330, and between proxy 330 and a database engine in database service 210, in order to ensure that communication with proxy is encrypted both for interactions clients 310 and with a database engine database service 210. Proxy node(s) 339 may implement routing lookup 336 to access database engine mapping 340 in order to locate, determine, or otherwise identify a network endpoint and thus a database engine to connect with in response to a connection request from a client 310, in some embodiments. In some embodiments, database engine mapping 340 may be stored as part of a separate database service that provides high-throughput and ensures consistent views of mapping information, in some embodiments (e.g., a NoSQL database service implemented as part of provider network 200).

Proxy nodes 330 may, in some embodiments, implement connection management 338 in order to manage the connections between proxy node 330 and various clients 310 and various database engines in database service 210. For example, connection management 338 may implement or impose various limitations on connection requests. In some embodiments, connection management 338 may freeze, block, or otherwise indicate (e.g., to load balancer 320) that a proxy node 330 is no longer accepting connections, in some embodiments. In some embodiments, connection management may implement various techniques to disconnect or otherwise end connections with either a database engine or client. In some embodiments, proxy node(s) 330 may be multi-tenant. For example, proxy nodes 330 may maintain connections with different clients and different database engines for different databases (e.g., associated with different user accounts of database service 210 or provider network 200), and thus may be multi-tenant proxy nodes. In some embodiments, connection management 338 may implement various security mechanisms or controls to ensure that data for different connections is isolated.

Proxy service 230 may implement proxy node management 350 in various embodiments, to provision, support, or otherwise maintain a pool of proxy nodes 330 for providing access to database service 210. For example, proxy node management 350 may start, launch or provision new proxy nodes if the number of proxy nodes (or potential connections supported) falls below a threshold amount, proxy node management 350 may add proxy nodes 330 to the pool. In some embodiments, proxy node management 350 may restart or shutdown proxy nodes (e.g., suspected of malicious behavior or under attack from malicious requests).

FIG. 4 is a logical block diagram illustrating a database service that implements proxy-based database scaling, according to some embodiments. Database service 210 may implement respective database engine head nodes, which may be provisioned, launched, connected, or otherwise assigned to provide access to a database stored in storage service 220, such as assigned database engine head nodes 420 a, 420 b, and 420 c, according to connections from proxy nodes 450 which act as clients on behalf clients that are connected with proxy node(s) 450, as discussed above. Proxy node(s) 450 may access a database engine head node 420 via a network (e.g., these components may be network-addressable and accessible to the clients 450 a-450 n), in some embodiments. Storage service 220, which may be employed by the database system to store data pages of one or more database tables (and redo log records and/or other metadata associated therewith), and to perform other functions of the database system as described herein, may or may not be network-addressable and accessible to proxy node(s) 450, in different embodiments. For example, in some embodiments, storage service 220 may perform various storage, access, change logging, recovery, and/or space management operations in a manner that is invisible to proxy node(s) 450.

Database engine head node 420 may receive requests from various client programs (e.g., applications) and/or subscribers (users) via proxy node(s) 450, then parse them, optimize them, and develop an execution plan to carry out the associated database operation(s), in some embodiments. In the example illustrated in FIG. 4, a query parsing, optimization, and execution component 405 of database engine head 420 may perform these functions for queries that are received from proxy node 450 and interact with database engine head node 420 via connection established by proxy node(s) 450. In some embodiments, the query parsing, optimization, and execution component 405 may return query responses to proxy node 450, which may include write acknowledgements, requested data pages (or portions thereof), error messages, and or other responses, as appropriate. As illustrated in this example, database engine head node 420 may also include a client-side storage service driver 425, which may route read requests and/or change notifications (e.g., redo log records) to various storage nodes within storage service 220, as discussed below, receive write acknowledgements from storage service 220, receive requested data pages from storage service 220, and/or return data pages, error messages, or other responses to the query parsing, optimization, and execution component 405 (which may, in turn, return them to proxy node 450). In some embodiments, client-side storage driver 425 may have access to storage metadata. Storage metadata may provide an access scheme for obtaining or writing to distributed storage service 410 (e.g., mapping information to one or more components within storage service 410 storing data for database system 400). When routing read or write requests to storage service 410, client-side storage driver 448 may access storage metadata to determine the particular storage nodes to send read or write requests to.

In this example, database engine head node 420 includes data page cache 435, in which data pages that were recently accessed (read and/or write) may be temporarily held. As illustrated in FIG. 4, database engine head node 420 may also include transaction and consistency management component 430, which may be responsible for providing transactionality and consistency in the database instance of which database engine head node 420 is a component. For example, this component may be responsible for ensuring the Atomicity, Consistency, and Isolation properties of the database instance and the transactions that are directed that the database instance. As illustrated in FIG. 4, database engine head node 420 may also include transaction log 440 and undo log 445, which may be employed by transaction and consistency management component 430 to track the status of various transactions and roll back any locally cached results of transactions that do not commit.

Database service 210 may implement warm pool 460, which may include one or more standby database engine head nodes 462. These standby database engine head nodes may be ready for provisioning according to the techniques discussed below with regard to FIGS. 8-9B. Database service 210 may implement control plane 470 to perform various management operations for database engine head nodes, including head node provisioning 472 and automated scaling 474, as discussed below with regard to FIGS. 8-11. In some embodiments, automated scaling 474 may implement a performance metrics store to apply machine learning techniques in order to identify scaling event criteria for a database.

For example, database workload metrics may be collected over time across different resource utilizations (e.g., network bandwidth utilization, processor utilization, I/O operations throughput or utilization, query types (e.g., read or write operations, among other metrics). Time series analysis may be performed with respect to the one or more resource utilization metrics to identify features of a change in workload that are particular to the database, in some embodiments. Then, similar features or criteria may be applied by automated scaling 474 in order to trigger scaling events for the database according to the features or criteria, in some embodiments. In this way, automated scaling may be adapted for the database over time and be applied in ways particular to an individual database, customizing scaling events and responses (e.g., how to change resources provisioned for the database) and because of the proxy-based scaling techniques discussed above and below such custom scaling events can be leveraged without disrupting clients that utilize the database while the database is undergoing a scaling event, in some embodiments.

In some embodiments, a storage device may refer to a local block storage volume as seen by the storage node, regardless of the type of storage employed by that storage volume, e.g., disk, a solid-state drive, a battery-backed RAM, an NVMRAM device (e.g., one or more NVDIMMs), or another type of persistent storage device. An storage device is not necessarily mapped directly to hardware. For example, a single storage device might be broken up into multiple local volumes where each volume is split into and striped across multiple segments, and/or a single drive may be broken up into multiple volumes simply for ease of management, in different embodiments. In some embodiments, each storage device may store an allocation map at a single fixed location. This map may indicate which storage pages that are owned by particular segments, and which of these pages are log pages (as opposed to data pages). In some embodiments, storage pages may be pre-allocated to each segment so that forward processing may not need to wait for allocation. Any changes to the allocation map may need to be made durable before newly allocated storage pages are used by the segments.

FIG. 5 is a logical block diagram illustrating a storage service that stores data for a separate database service, according to some embodiments. A database engine head node 510 may include a client-side storage service driver 512. Storage service 220 may implement, in various embodiments, multiple storage nodes (including those shown as 530, 540, and 550), each of which includes storage for data pages, redo logs for the segment(s) it stores, system metadata for database engine head 510 (e.g., data dictionary data, transaction table data etc.) and hardware and/or software may perform various segment management functions. For example, each storage node may include hardware and/or software may perform at least a portion of any or all of the following operations: replication (locally, e.g., within the storage node), coalescing of redo logs to generate data pages, crash recovery, and/or space management (e.g., for a segment). Each storage node may also have multiple attached storage devices (e.g., SSDs) on which data blocks may be stored on behalf of clients (e.g., users, client applications, and/or database service subscribers), in some embodiments.

In the example illustrated in FIG. 5, storage node 530 includes data page(s) 533, segment redo log(s) 535, segment management functions 537, and attached storage devices 571-578. Similarly, storage node 540 includes data page(s) 543, segment redo log(s) 545, segment management functions 547, and attached storage devices 581-588; and storage node 550 includes data page(s) 553, segment redo log(s) 555, segment management functions 557, and attached storage devices 591-598.

Storage service 220 may implement storage service control plane 520 to perform various service management operations, in some embodiments. In at least some embodiments, storage service control plane 520 may implement volume management 522 which may be implemented to create database volumes for new databases, facilitate opening and closing of database volumes by clients, and/or recovery operations, in some embodiments.

FIG. 6 is a logical block diagram illustrating example client interactions to configure scaling events for a database, according to some embodiments. Database service control plane 470 may implement an interface 602 (e.g., a graphical user interface hosted as part of a service console and/or programmatic interface (API)) via which a client 600 (e.g., an application, such as a web browser, that enables a user to access a control console implemented as part of interface 602 or a database application that can configure and/or access a database on behalf of a user) can submit a request to establish or modify databases that are managed, in some embodiments. For example, client 600 may submit a request to create 610 a managed database, in some embodiments. The creation request 610 may specify an initial database engine configuration or information for accessing the database. In some embodiments, the request may specific scaling event criteria (e.g., by selecting features to optimize for, such as speed or low cost).

Similarly, in some embodiments, client 610 may explicitly specify scaling event criteria for a managed database, as indicated at 620. For example, client 600 can modify thresholds, change resources selected for optimization, block or deny scaling events for particular times or for particular users by a request 620, in some embodiments. In some embodiments, as indicated at 630, client 610 may send a request for a scaling operation. For example, a manual scaling operation may be requested to increase or decrease the resource capacity (e.g., CPU, memory, connections, etc.) so that a database engine head node with those capabilities is provisioned and scaled to, in some embodiments. As indicated at 640, scaling event metrics 640 may be provided to a client 600 (e.g., indicating when the event happened, what criteria were triggered, what configuration was scaled to, cost changes, etc.), in some embodiments.

FIG. 7 is a block diagram illustrating the use of a separate storage service for a database service accessed via a proxy service, according to some embodiments. In this example, one or more client processes 710 may store data to one or more databases maintained by a database system that includes a database engine head node 720 and a storage service 220. In the example illustrated in FIG. 7, database engine 7 head node 20 includes database tier components 750 and client-side driver 740 (which serves as the interface between storage service 220 and database tier components 760). In some embodiments, database tier components 750 may perform functions such as those performed by query parsing, optimization and execution component 405 and transaction and consistency management component 430 of FIG. 4, and/or may store data pages, transaction logs and/or undo logs (such as those stored by data page cache 435, transaction log 440 and undo log 445 of FIG. 4).

In this example, one or more client processes 710 may send database query requests 715 (which may include read and/or write requests targeting data stored on one or more of the storage nodes 735 a-735 n) to a connected proxy node 760. Proxy node 760 may route the database query requests 715 to database tier components 750, and may receive database query responses 717 from database tier components 750 (e.g., responses that include write acknowledgements and/or requested data) and return them 719 to client processes 710. Each database query request 713 that includes a request to write to a page may be parsed and optimized to generate one or more write record requests 741, which may be sent to client-side driver 740 for subsequent routing to storage service 220. In this example, client-side driver 740 may generate one or more redo log records 731 corresponding to each write record request 741, and may send them to specific ones of the storage nodes 735 of storage service 220. Storage service 220 may return a corresponding write acknowledgement 723 for each redo log record 731 to database engine head node 720 (specifically to client-side driver 740). Client-side driver 740 may pass these write acknowledgements to database tier components 750 (as write responses 742), which may then send corresponding responses (e.g., write acknowledgements) to one or more client processes 710 as one of database query responses 719.

In this example, each database query request 713 that includes a request to read a data page may be parsed and optimized to generate one or more read record requests 743, which may be sent to client-side driver 740 for subsequent routing to storage service 220. In this example, client-side driver 740 may send these requests to specific ones of the storage nodes 735 of storage service 220, and storage service 220 may return the requested data pages 733 to database engine head node 720 (specifically to client-side driver 740). Client-side driver 740 may send the returned data pages to the database tier components 750 as return data records 744, and database tier components 750 may then send 717 the data pages to proxy node 760 which may return the results to one or more client processes 710 as database query responses 719.

In some embodiments, various error and/or data loss messages 734 may be sent from storage service 220 to database engine head node 720 (specifically to client-side driver 740). These messages may be passed from client-side driver 740 to database tier components 760 as error and/or loss reporting messages 745, and then to one or more client processes 710 along with (or instead of) a database query responses 717 and 719.

In some embodiments, the APIs 731-734 of storage service 220 and the APIs 741-745 of client-side driver 740 may expose the functionality of the storage service 220 to database engine head node 720 as if database engine 720 were a client of storage service 220. For example, database engine head node 720 (through client-side driver 740) may write redo log records or request data pages through these APIs to perform (or facilitate the performance of) various operations of the database system implemented by the combination of database engine head node 720 and storage service 220 (e.g., storage, access, change logging, recovery, and/or space management operations). As illustrated in FIG. 7, storage service 220 may store data blocks on storage nodes 735 a-735 n, each of which may have multiple attached SSDs. In some embodiments, storage service 220 may provide high durability for stored data block through the application of various types of redundancy schemes.

Note that in various embodiments, the API calls and responses between database engine head node 720 and storage service 220 (e.g., APIs 731-734) and/or the API calls and responses between client-side driver 740 and database tier components 750 (e.g., APIs 741-745) and the calls and responses 715 and 717 between proxy node 760 and database tier components 750 in FIG. 7 may be performed over a secure proxy connection (e.g., one managed by a gateway control plane), or may be performed over the public network or, alternatively, over a private channel such as a virtual private network (VPN) connection. These and other APIs to and/or between components of the database systems described herein may be implemented according to different technologies, including, but not limited to, Simple Object Access Protocol (SOAP) technology and Representational state transfer (REST) technology. For example, these APIs may be, but are not necessarily, implemented as SOAP APIs or RESTful APIs. SOAP is a protocol for exchanging information in the context of Web-based services. REST is an architectural style for distributed hypermedia systems. A RESTful API (which may also be referred to as a RESTful web service) is a web service API implemented using HTTP and REST technology. The APIs described herein may in some embodiments be wrapped with client libraries in various languages, including, but not limited to, C, C++, Java, C #and Perl to support integration with database engine head node 720 and/or storage service 220.

FIG. 8 is sequence diagram illustrating a scaling event to change between different database engines, according to some embodiments. As indicated at 810, database requests 840 may be sent to a proxy node 810 connected to current database engine head node 830. A scaling event may be detected for the database by automated scaling 474, as discussed below with regard to FIGS. 10 and 11. Automated scaling 474 may provision 842 a new database engine head node 820 and signal 844 to current database engine head node to prepare for a scaling event. Current database engine head node 830 may determine a safe place to quit performance of database requests 840 (e.g., between transactions) and send scaling information (e.g., identity of new database engine head node 820), unperformed database requests (e.g., after the safe point), and session state information 848 to proxy node 810. In some embodiments, scaling information may be sent to proxy node 810 in response to a request for scaling information sent from proxy node 810 to database engine head node 830. For example, proxy node 810 may detect a lag in database requests 840 received from clients of the database, and thus may send a request to database engine head node 830 which would trigger the return of scaling information (if a scaling event was ongoing or a return of no information if no scaling event was ongoing, e.g., by sending a special status packet that would trigger the return of scaling information if existent). In some embodiments, automated scaling 474 may send an indication 474 to proxy node 810 to indicate the scaling event for the database.

Proxy node 810 may establish a connection 850 with new database engine head node 820, and copy 852 session state 820 and other information like unperformed requests to new database engine head node 820. Alternatively, in some embodiments, proxy node 810 may wait until current database engine head node 830 has completed all outstanding requests before connecting to new database engine head node 820 (e.g., by sending a test or other “fake” packet that would be returned to the proxy node from current database engine head node that all other requests received before that packet have been performed) (not illustrated). New database engine head node 820 may perform the unperformed requests (using the copied session state) and provide results 854 to proxy node 810. Proxy node 810 may then provide results 856 to a client (which may not be aware of the change in database engine head nodes, in some embodiments). Proxy node 810 may also close 858 the connection with database engine head node 830.

FIGS. 9A and 9B are sequence diagrams to enter and exit a hibernation state for database using scaling events for the database, according to some embodiments. Proxy node 910 may have established a connection with current database engine head node 920 to provide access to a database. A scaling event that triggers a hibernation state for the database engine head node may be detected, and automated scaling 474 may send a request to current database engine head node 920 to prepare for hibernation scaling event, as indicated at 940. Current database engine head node 920 may send session state information 942 to proxy node 910. Proxy node 910 may then close the connection 944 with current database engine head node 920 so that no resources are consumed to wait for access requests to the database (e.g., as proxy node 910 may be multi-tenant), and thus the database enters hibernation period 990.

As illustrated in FIG. 9B, a database request 950 may result in bringing the database out of database hibernation period 990. The database request 950 may be received at proxy node 910 which may send a request for a new database engine head node 952 to automated scaling 474. Automated scaling 474 may identify and provision a new head node for the wakeup scaling event 854, such as new database engine head node 930. Automated scaling may identify 956 the new head node to proxy node 910. Proxy node 910 may then establish a connection 958 with new database engine head node 930. Proxy node 910 may then copy a stored copy of the session state to new database engine head node 930, as indicated at 960. In some embodiments, the session state may be encrypted or otherwise blocked from direct access of the contents by proxy node 910. Proxy node 910 may then send the database request 962 to the new database engine head node 930 to be performed. New database engine head node 930 may send a result 964, which proxy node 910 may return 966 to a client.

The database service, proxy service, and storage service discussed in FIGS. 2 through 9B provide examples of a system that may implement proxy-based scaling for a database. However, various other types of database systems may implement proxy-based scaling for a database. For example, other kinds of storage systems (e.g., non-log-based data stores or data stores that are not distributed) may provide backend storage for connecting different database engines. FIG. 10 is high-level flowchart illustrating various methods and techniques to implement proxy-based database scaling, according to some embodiments. Various different systems and devices may implement the various methods and techniques described below, either singly or working together. For example, a proxy node and/or control plane for a database service as discussed above may implement the various methods. Alternatively, a combination of different systems and devices may implement the various methods. Therefore, the above examples and or any other systems or devices referenced as performing the illustrated method, are not intended to be limiting as to other different components, modules, systems, or configurations of systems and devices.

As indicated at 1010, a database accessed by a proxy connected to a client may be monitored for a scaling event, in various embodiments. For example, various different thresholds, statistics, patterns, or other criteria across one or more performance metrics, environmental or system state, or other information indicative of performance of access to a database may be analyzed or evaluated, in some embodiments. CPU utilization of a host system (e.g., a server) for a database engine may measure or compared based on percentage utilized and/or credits or other units of work performed by the CPU for the database engine with a threshold (e.g., if percentage utilization is less than 10% scale down to a database engine on a host with a smaller processor capacity, or enter a hibernate state), in some embodiments. Connection utilization for a database engine (e.g., percentage or number of available connections to the database at the database engine), may be evaluated, in some embodiments (e.g., if connection utilization is at 100%, then scale up to a database engine on a host with a greater number of possible connections). Similar other resources for a database engine, such as network bandwidth, buffer pool size, or memory may be evaluated, in some embodiments.

Various models or techniques may be performed in order to evaluate or characterize the performance of a resource. For example, CPU and network may both subject to queuing because as these resources approach being fully utilized, a performance hit may be taken in terms of queuing latency to utilize the resources, in some embodiments. CPU may exhibit further constraint so that scaling can only add “ability” to do more parallel work”, and not higher-CPU megahertz, in some embodiments. In some embodiments, queue modeling may estimate if there is queuing based on long-term average utilization. In some embodiments, queue modeling may estimate percentage time of saturation (e.g., times when there was no free resource. In some embodiments, queuing may be directly measured. In some embodiments, free execution units may be evaluated (e.g., if a system has a whole execution unit free (that is, a full core) most of the time then it probably isn't experiencing queuing).

Saturation may be used to estimate queuing, in some embodiments, by measuring the percentage of time when there is little to no free capacity, for example, measuring when the percentage of time when instantaneous utilization is 100%. In some embodiments, saturation can be estimated by measuring utilization on a higher frequency, and then evaluating how often utilization is above a threshold (rather than simply averaging). For example, over 10 samples in a 1 second period, 5 samples may be at 90% utilized and 5 samples may be at 50% utilized, indicates that the system may be more saturated than if 10 samples were at 70% utilized, even though both measures have the same overall utilization.

In some embodiments, queuing may be modeled by looking at thread states. At any point of time, threads may not be running because the thread is unable to run (e.g. suspended, IO/wait, etc.), because a CPU core is not available (runnable but not running), or actually running. Most operating systems may indicate in a report if a thread is runnable, and some operating systems distinguish between runnable and not running and runnable and running, in some embodiments. Runnable threads minus a number of cores may indicate how many threads there are that could have benefitted from additional CPU cores, in some embodiments for detecting a scaling event.

For resources that suffer from capacity related performance concerns that may warrant a scaling event, other techniques may be used, in some embodiments. For example, memory implementing a cache, like a buffer pool, may have a performance problem when the size of the working set does not fit. The effect of a too-small cache may be an increased miss rate, and hence more time spent waiting for data to be fetched from the (presumably) slower primary storage, in some embodiments. If the miss rate is very low, there is likely little benefit to a larger cache, and thus a scaling event may not be triggered, in such a scenario, in some embodiments. A high miss rate can be a large performance opportunity for a larger cache, in some embodiments. Consider a workload which is random among 100 gigabytes. If there is a 50 gigabyte buffer pool, there may be 50% miss rate; since hits may be measured in microseconds and misses are roughly 10 milliseconds, resulting in a per-query latency of approximately 5 milliseconds on average. If the size of the buffer pool were doubled, then the miss rate may drop to 0, and latency may only be a few hundred microseconds, resulting in a 20× performance increase for merely 2× the cost if a scaling event is triggered and successfully performed.

In some scenarios, a larger cache may not be beneficial and thus scaling criteria may be designed to prevent a scaling event in such a case, such as when the working set is very large. Consider, for instance, a workload which is scans of an entire data set. A larger cache would not help because a scan would not benefit from the cache. In another example of a workload which uses sequential scans, most accesses will be a miss because a pattern of access to perform the sequential scans could trigger bad cache management behavior.

A miss rate curve may be evaluated as part of scaling criteria, in some embodiments. The miss rate curve may show how a workload behaves as the cache size changes, in some embodiments. If the miss rate curve is estimated, the performance benefit (or penalty) of growing (or shrinking) the buffer pool can be better predicted, in some embodiments.

Scaling event criteria may be used to detect scaling events, either singly or various combinations. As discussed above with regard to FIG. 4, various machine learning techniques may be applied to determine scaling event criteria for a database based on the past performance of requests to access the database (e.g., using different types of database engines, results of scaling events, etc.). In some embodiments, a scaling event may be manually triggered based on a user request. In some embodiments, a scaling event may be triggered according to a schedule (e.g., hibernate from midnight to 6:00 am).

Scaling vent criteria may, in some embodiments, identify the desired configuration of the database engine to scale to. For example, scaling criteria may indicate which resource on the host of a new database engine needs to be increased (e.g., memory, CPU, network bandwidth, and so on). In some embodiments, desired configurations may be ranked with available database engines that have some or all of the desired configuration. In some embodiments, a scaling event may be aborted if a database engine with desired configuration is unavailable (or delayed until one is available).

If no scaling event is detected, as indicated by the negative exit from 1020, monitoring may continue. If a scaling event is detected, then as indicated by the positive exit from 1020, a connection between the proxy and a first database engine may be established to provide access to the database, as indicated at 1030, in some embodiments. For example, database connection communications or protocols (e.g., to establish a secure or encrypted communication channel, as discussed below) may be performed between the proxy and the database engine so that the proxy can direct requests to perform database queries through the second network endpoint to the database engine, in some embodiments.

As indicated at 1040, session state from a second database that previously provided access to the database may be copied to the first database engine, in some embodiments. For example, the proxy may obtain the session state from the second database engine while the second database engine is still connected the proxy, as illustrated in FIG. 8, or before disconnecting from the second database engine, as illustrated in FIG. 9A. In some embodiments, session state may include various information that informs the processing of requests to the database (e.g., database statistics, cache contents, users, access controls, etc.). The first database engine may ingest or otherwise apply the session state to make the first database engine appear to a client connected via the proxy that the client was connected to the same database engine (instead of a different database engine), in some embodiments.

Requests to access the database may then be performed using the established connection with the first database engine. As illustrated in FIG. 10, scaling may be performed multiple times for a same database in response to detecting a scaling event.

FIG. 11 is high-level flowchart illustrating various methods and techniques to handle database access requests for a database in hibernation state, according to some embodiments. As indicated at 1110, a database request may be received from a client a proxy, in some embodiments. For example, a request to access a database formatted according to an API or other interface, protocol, or language (e.g., Structured Query Language) may be received at the proxy (e.g., a query for data in the database or a request to update, add, or remove data from the database), in some embodiments. The proxy may maintain state or other information describing the status of a databases of the clients connected to the proxy. For example, a proxy may maintain a status table that indicates that a client connected to the proxy is connected to access a database that is in a hibernated state (as discussed above with regard to FIGS. 9A-9B). In some embodiments, the proxy may parse the database request, as indicated at 1120, if the database to which the request is directed is in a hibernation state, whereas in other embodiments, the database request may be parsed at the proxy with regard to the state of the targeted database.

An evaluation of whether the proxy is able to perform the database request may be performed, in some embodiments, as indicated at 1130. For example, the proxy may be able to determine from the parsed query that it is a query that does not require access to database data in order to be performed (e.g., a “SELECT 1” query or other request often used to determine whether the database connection is alive). In some embodiments, the parsed request may refer to database table statistics or schema information (e.g., a request to describe a table in the database) for which the proxy has obtained the statistics or schema information to answer the query (which may be provided as part of the session state or along with the session state). In some embodiments, the proxy may be able to be able access a portion of database contents provided as part of session state (e.g., portions of a buffer cache or query results cache), in some embodiments.

If the proxy is able to perform the database request, then as indicated at 1140, the proxy may perform the database request, in some embodiments. For example, the proxy may implement a light-weight query engine or other component capable of parsing database data (e.g., table data) or metadata (e.g., schema or statistics) in order to provide a response). In some embodiments, the proxy may be able to recognize the request and access an answer table or other mapping that maps the request to the appropriate result (without having to perform or implement a query engine), such as mapping liveness requests like “SELECT 1” to the appropriate result. As indicated at 1150, the proxy may return a result for the database request to the client, in some embodiments.

If the proxy is not able to perform the database request, then the database may be transitioned out of hibernation state, in some embodiments, in order to perform the database request. For example, as indicated at 1142, a database engine may be provisioned for the database, in some embodiments. A warm pool of standby database engines which are not yet provisioned or assigned may, for instance, be used to select a database engine. The selected database engine may conform to a predetermined performance configuration or profile (e.g., based configuration settings for a managed database or other setting specified by a user), in some embodiments. The provisioned database engine may be provided with the appropriate credentials to access data in a separate network-based data store, such as the storage service 220 in FIG. 2, in some embodiments. The provisioned database engine may be provided with encryption or other security information to establish secured communication with the proxy, in some embodiments.

As indicated at 1152, a connection may be established between the proxy and the provisioned database engine, in some embodiments. As indicated at 1162, session state obtained from a previous database engine and stored at the proxy may be sent to the provisioned database engine, in some embodiments. As indicated at 1172, the database request may be sent to the provisioned database engine via the connection, in some embodiments. As indicated at 1182, a result of the database request received from the provisioned database engine at the proxy may be returned to the client, in some embodiments.

FIG. 12 is a block diagram illustrating an example computer system, according to various embodiments. For example, computer system 2000 may implement a proxy node, database engine head node, or one of a plurality of storage nodes of a separate distributed storage system that stores database tables and associated metadata on behalf of clients, in various embodiments. Computer system 2000 may be any of various types of devices, including, but not limited to, a personal computer system, desktop computer, laptop or notebook computer, mainframe computer system, handheld computer, workstation, network computer, a consumer device, application server, storage device, telephone, mobile telephone, or in general any type of computing device.

Computer system 2000 includes one or more processors 2010 (any of which may include multiple cores, which may be single or multi-threaded) coupled to a system memory 2020 via an input/output (I/O) interface 2030. Computer system 2000 further includes a network interface 2040 coupled to I/O interface 2030. In various embodiments, computer system 2000 may be a uniprocessor system including one processor 2010, or a multiprocessor system including several processors 2010 (e.g., two, four, eight, or another suitable number). Processors 2010 may be any suitable processors capable of executing instructions. For example, in various embodiments, processors 2010 may be general-purpose or embedded processors implementing any of a variety of instruction set architectures (ISAs), such as the x86, PowerPC, SPARC, or MIPS ISAs, or any other suitable ISA. In multiprocessor systems, each of processors 2010 may commonly, but not necessarily, implement the same ISA. The computer system 2000 also includes one or more network communication devices (e.g., network interface 2040) for communicating with other systems and/or components over a communications network (e.g. Internet, LAN, etc.). For example, a client application executing on system 2000 may use network interface 2040 to communicate with a server application executing on a single server or on a cluster of servers that implement one or more of the components of the database systems described herein. In another example, an instance of a server application executing on computer system 2000 may use network interface 2040 to communicate with other instances of the server application (or another server application) that may be implemented on other computer systems (e.g., computer systems 2090).

In the illustrated embodiment, computer system 2000 also includes one or more persistent storage devices 2060 and/or one or more I/O devices 2080. In various embodiments, persistent storage devices 2060 may correspond to disk drives, tape drives, solid state memory, other mass storage devices, or any other persistent storage device. Computer system 2000 (or a distributed application or operating system operating thereon) may store instructions and/or data in persistent storage devices 2060, as desired, and may retrieve the stored instruction and/or data as needed. For example, in some embodiments, computer system 2000 may host a storage system server node, and persistent storage 2060 may include the SSDs attached to that server node.

Computer system 2000 includes one or more system memories 2020 that may store instructions and data accessible by processor(s) 2010. In various embodiments, system memories 2020 may be implemented using any suitable memory technology, (e.g., one or more of cache, static random access memory (SRAM), DRAM, RDRAM, EDO RAM, DDR 10 RAM, synchronous dynamic RAM (SDRAM), Rambus RAM, EEPROM, non-volatile/Flash-type memory, or any other type of memory). System memory 2020 may contain program instructions 2025 that are executable by processor(s) 2010 to implement the methods and techniques described herein. In various embodiments, program instructions 2025 may be encoded in platform native binary, any interpreted language such as Java™ byte-code, or in any other language such as C/C++, Java™, etc., or in any combination thereof. In some embodiments, program instructions 2025 may implement multiple separate clients, server nodes, and/or other components.

In some embodiments, program instructions 2025 may include instructions executable to implement an operating system (not shown), which may be any of various operating systems, such as UNIX, LINUX, Solaris™, MacOS™, Windows™, etc. Any or all of program instructions 2025 may be provided as a computer program product, or software, that may include a non-transitory computer-readable storage medium having stored thereon instructions, which may be used to program a computer system (or other electronic devices) to perform a process according to various embodiments. A non-transitory computer-readable storage medium may include any mechanism for storing information in a form (e.g., software, processing application) readable by a machine (e.g., a computer). Generally speaking, a non-transitory computer-accessible medium may include computer-readable storage media or memory media such as magnetic or optical media, e.g., disk or DVD/CD-ROM coupled to computer system 2000 via I/O interface 2030. A non-transitory computer-readable storage medium may also include any volatile or non-volatile media such as RAM (e.g. SDRAM, DDR SDRAM, RDRAM, SRAM, etc.), ROM, etc., that may be included in some embodiments of computer system 2000 as system memory 2020 or another type of memory. In other embodiments, program instructions may be communicated using optical, acoustical or other form of propagated signal (e.g., carrier waves, infrared signals, digital signals, etc.) conveyed via a communication medium such as a network and/or a wireless link, such as may be implemented via network interface 2040.

In some embodiments, system memory 2020 may include data store 2045, as described herein. For example, the information described herein as being stored by the database tier (e.g., on a primary node), such as a transaction log, an undo log, cached page data, or other information used in performing the functions of the database tiers described herein may be stored in data store 2045 or in another portion of system memory 2020 on one or more nodes, in persistent storage 2060, and/or on one or more remote storage devices 2070, at different times and in various embodiments. Along those lines, the information described herein as being stored by a read replica, such as various data records stored in a cache of the read replica, in-memory data structures, manifest data structures, and/or other information used in performing the functions of the read-only nodes described herein may be stored in data store 2045 or in another portion of system memory 2020 on one or more nodes, in persistent storage 2060, and/or on one or more remote storage devices 2070, at different times and in various embodiments. Similarly, the information described herein as being stored by the storage tier (e.g., redo log records, data pages, data records, and/or other information used in performing the functions of the distributed storage systems described herein) may be stored in data store 2045 or in another portion of system memory 2020 on one or more nodes, in persistent storage 2060, and/or on one or more remote storage devices 2070, at different times and in various embodiments. In general, system memory 2020 (e.g., data store 2045 within system memory 2020), persistent storage 2060, and/or remote storage 2070 may store data blocks, replicas of data blocks, metadata associated with data blocks and/or their state, database configuration information, and/or any other information usable in implementing the methods and techniques described herein.

In one embodiment, I/O interface 2030 may coordinate I/O traffic between processor 2010, system memory 2020 and any peripheral devices in the system, including through network interface 2040 or other peripheral interfaces. In some embodiments, I/O interface 2030 may perform any necessary protocol, timing or other data transformations to convert data signals from one component (e.g., system memory 2020) into a format suitable for use by another component (e.g., processor 2010). In some embodiments, I/O interface 2030 may include support for devices attached through various types of peripheral buses, such as a variant of the Peripheral Component Interconnect (PCI) bus standard or the Universal Serial Bus (USB) standard, for example. In some embodiments, the function of I/O interface 2030 may be split into two or more separate components, such as a north bridge and a south bridge, for example. Also, in some embodiments, some or all of the functionality of I/O interface 2030, such as an interface to system memory 2020, may be incorporated directly into processor 2010.

Network interface 2040 may allow data to be exchanged between computer system 2000 and other devices attached to a network, such as other computer systems 2090 (which may implement one or more storage system server nodes, primary nodes, read-only node nodes, and/or clients of the database systems described herein), for example. In addition, network interface 2040 may allow communication between computer system 2000 and various I/O devices 2050 and/or remote storage 2070. Input/output devices 2050 may, in some embodiments, include one or more display terminals, keyboards, keypads, touchpads, scanning devices, voice or optical recognition devices, or any other devices suitable for entering or retrieving data by one or more computer systems 2000. Multiple input/output devices 2050 may be present in computer system 2000 or may be distributed on various nodes of a distributed system that includes computer system 2000. In some embodiments, similar input/output devices may be separate from computer system 2000 and may interact with one or more nodes of a distributed system that includes computer system 2000 through a wired or wireless connection, such as over network interface 2040. Network interface 2040 may commonly support one or more wireless networking protocols (e.g., Wi-Fi/IEEE 802.11, or another wireless networking standard). However, in various embodiments, network interface 2040 may support communication via any suitable wired or wireless general data networks, such as other types of Ethernet networks, for example. Additionally, network interface 2040 may support communication via telecommunications/telephony networks such as analog voice networks or digital fiber communications networks, via storage area networks such as Fibre Channel SANs, or via any other suitable type of network and/or protocol. In various embodiments, computer system 2000 may include more, fewer, or different components than those illustrated in FIG. 12 (e.g., displays, video cards, audio cards, peripheral devices, other network interfaces such as an ATM interface, an Ethernet interface, a Frame Relay interface, etc.)

It is noted that any of the distributed system embodiments described herein, or any of their components, may be implemented as one or more network-based services. For example, a read-write node and/or read-only nodes within the database tier of a database system may present database services and/or other types of data storage services that employ the distributed storage systems described herein to clients as network-based services. In some embodiments, a network-based service may be implemented by a software and/or hardware system designed to support interoperable machine-to-machine interaction over a network. A web service may have an interface described in a machine-processable format, such as the Web Services Description Language (WSDL). Other systems may interact with the network-based service in a manner prescribed by the description of the network-based service's interface. For example, the network-based service may define various operations that other systems may invoke, and may define a particular application programming interface (API) to which other systems may be expected to conform when requesting the various operations.

In various embodiments, a network-based service may be requested or invoked through the use of a message that includes parameters and/or data associated with the network-based services request. Such a message may be formatted according to a particular markup language such as Extensible Markup Language (XML), and/or may be encapsulated using a protocol such as Simple Object Access Protocol (SOAP). To perform a network-based services request, a network-based services client may assemble a message including the request and convey the message to an addressable endpoint (e.g., a Uniform Resource Locator (URL)) corresponding to the web service, using an Internet-based application layer transfer protocol such as Hypertext Transfer Protocol (HTTP).

In some embodiments, network-based services may be implemented using Representational State Transfer (“RESTful”) techniques rather than message-based techniques. For example, a network-based service implemented according to a RESTful technique may be invoked through parameters included within an HTTP method such as PUT, GET, or DELETE, rather than encapsulated within a SOAP message.

Although the embodiments above have been described in considerable detail, numerous variations and modifications may be made as would become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such modifications and changes and, accordingly, the above description to be regarded in an illustrative rather than a restrictive sense. 

1-20. (canceled)
 21. A system, comprising: one or more processors; and a memory, that stores program instructions that, when executed by the at least one processor, cause the one or more processors to implement a proxy for a database engine, configured to: receive a request for a database; determine that the proxy is able to perform the database request instead of using the database engine to perform the request; perform the request for the database; and return a result for the request for the database.
 22. The system of claim 21, wherein the proxy is further configured to: receive a second request for the database; determine that the proxy is not able to perform the second database request; establish a connection between the proxy and the database engine; send the second request for the database to the database engine; and return a second result for the second request for the database received from the database engine at the proxy.
 23. The system of claim 22, wherein the proxy is further configured to provision the database engine from a pool of standby database engines after determining that the proxy is not able to perform the second database request.
 24. The system of claim 22, wherein the proxy is further configured to send session state obtained from a previous database engine and stored at the proxy to the database engine.
 25. The system of claim 21, wherein to determine that the proxy is able to perform the database request, the proxy is configured to determine that session state received at the proxy from a prior database engine for the database comprises the results for the request and wherein to perform the database request, the proxy is configured to access the session state.
 26. The system of claim 21, wherein to determine that the proxy is able to perform the database request, the proxy is configured to recognize that the request can be performed using a mapping to the result for the request and wherein to perform the database request, the proxy is configured to use the mapping to access the result according to the mapping.
 27. The system of claim 21, wherein the proxy, the database engine and the database are implemented as part of one or more services hosted by a provider network.
 28. A method, comprising: receiving, at a proxy for a database engine, a request for a database; determining, by the proxy for the database engine, that the proxy is able to perform the database request instead of using the database engine to perform the request; performing, by the proxy for the database engine, the request for the database; and returning, by the proxy for the database engine, a result for the request for the database.
 29. The method of claim 28, further comprising: receiving, at the proxy for the database engine, a second request for the database; determining, by the proxy for the database engine, that the proxy is not able to perform the second database request; establishing, by the proxy for the database engine, a connection between the proxy and the database engine; sending, by the proxy for the database engine, the second request for the database to the database engine; and returning, by the proxy for the database engine, a second result for the second request for the database received from the database engine at the proxy.
 30. The method of claim 29, further comprising provisioning the database engine from a pool of standby database engines after determining that the proxy is not able to perform the second database request.
 31. The method of claim 29, further comprising sending, by the proxy for the database engine, session state obtained from a previous database engine and stored at the proxy to the database engine.
 32. The method of claim 28, wherein determining that the proxy is able to perform the database request comprises determining that session state received at the proxy from a prior database engine for the database comprises the results for the request and wherein performing the database request comprises accessing the session state.
 33. The method of claim 28, wherein determining that the proxy is able to perform the database request comprises recognizing that the request can be performed using a mapping to the result for the request and wherein performing the database request comprises using the mapping to access the result according to the mapping.
 34. The method of claim 28, wherein the proxy, the database engine and the database are implemented as part of one or more services hosted by a provider network.
 35. One or more non-transitory computer-readable storage media storing program instructions that, when executed on or across one or more processors, cause the one or more processors to: receiving, at a proxy for a database engine, a request for a database; determining, by the proxy for the database engine, that the proxy is able to perform the database request instead of using the database engine to perform the request; performing, by the proxy for the database engine, the request for the database; and returning, by the proxy for the database engine, a result for the request for the database.
 36. The one or more non-transitory computer-readable storage media of claim 35, storing further program instructions that when executed on or across the one or more computing devices, cause the one or more computing devices to further implement: receiving, at the proxy for the database engine, a second request for the database; determining, by the proxy for the database engine, that the proxy is not able to perform the second database request; establishing, by the proxy for the database engine, a connection between the proxy and the database engine; sending, by the proxy for the database engine, the second request for the database to the database engine; and returning, by the proxy for the database engine, a second result for the second request for the database received from the database engine at the proxy.
 37. The one or more non-transitory computer-readable storage media of claim 36, storing further program instructions that when executed on or across the one or more computing devices, cause the one or more computing devices to further implement provisioning the database engine from a pool of standby database engines after determining that the proxy is not able to perform the second database request.
 38. The one or more non-transitory computer-readable storage media of claim 36, storing further program instructions that when executed on or across the one or more computing devices sending, by the proxy for the database engine, session state obtained from a previous database engine and stored at the proxy to the database engine.
 39. The one or more non-transitory computer-readable storage media of claim 35, wherein, in determining that the proxy is able to perform the database request, the program instructions cause the one or more computing devices to implement determining that session state received at the proxy from a prior database engine for the database comprises the results for the request and wherein, in performing the database request, the programming instructions cause the one or more computing devices to implement accessing the session state.
 40. The one or more non-transitory computer-readable storage media of claim 35, wherein, in determining that the proxy is able to perform the database request, the program instructions cause the one or more computing devices to implement recognizing that the request can be performed using a mapping to the result for the request and wherein, in performing the database request, the program instructions cause the one or more computing devices to implement using the mapping to access the result according to the mapping. 